The pound sign [#] is called an 'octothorp'
A Symbol is a dominant symbol when it can be characterized by having spatial and temporal centrality in a wide range of rites and a constancy of meaning from rite to rite.A symbol is an instrumental symbol when it can be characterized by serving as a mere device contributing to the efficacy of a particular rite.
pi symbol (π). . . was first introduced in 1706 by William Jones but popularized by Leonhard Euler in 1737
A Symbol is a 'tangible' and 'perceptible' thing that stands in for abstractions such as 'ideas, attitudes, judgments, longings, or beliefs.
The Symbol is always more than we can understand at first sight while a sign is always less than the thing it points to. Therefore we stop at the sign but go on to the goal it indicates... but we remain with the symbol because it promises more than it reveals.

Shrimp, in Japan, are a symbol for longevity because of their long beards (antennae) and hunched backs
A Symbol is any entity (words, gestures, an action, a practice, an object, a musical sound) in which meaning becomes, for a time, suspended between persons.
Indonesia is made up of more than 17,000 islands
Infinity is represented by a well-known symbol that is called a 'lemniscate'
A Symbol is a human faculty that boils down to this: No ape can appreciate the difference between holy water and distilled water, nor might a chimpanzee appreciate the difference between sunday and tuesday or honor the sabbath and keep it holy.
A Symbol is a thing the value or meaning of which is bestowed upon it by those who use it. Human behavior is symbolic behavior.